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The Plasma Membrane and its Function
Review
Use each of the terms below just once to complete the passage.
Glucose
Organism
plasma membrane
balance
homeostasis
selective permeability
Living cells maintain a (1) __________________ by controlling materials
that enter and leave. Without this ability, the cell cannot maintain (2)
_____________and will die. The cell must regulate internal concentrations of
water, (3) ______________________, and other nutrients and must eliminate
waste products. Homeostasis in a cell is maintained by the (4)
________________________, which allows only certain particles to pass
through and keeps other particles out. This property of a membrane is known as
(5) ________________________________. It allows different cells to carry on
different activities within the same (6) ________________________.
For each statement below write true or false.
___________1.
___________2.
___________3.
___________4.
___________5.
___________6.
___________7.
The structure and properties of the cell wall allow it to be
selective and maintain homeostasis.
The plasma membrane is a bilayer of lipid molecules with
protein molecules embedded in it.
A phospholipids molecule has a nonpolar water in-soluble
head attached to a long polar, soluble tail.
The fluid mosaic model describes the plasma membrane as a
structure that is liquid and very rigid.
Cell organelles, such as the nucleus, vacuoles, mitochondria
and chloroplasts are enclosed in membranes.
The greater the number of saturated fatty acids a membrane
contains, the more fluid it is.
In animals, cholesterol strengthens the fluid mosaic and
makes the plasma membrane more stable.
Circle the letter of the choice that best completes the statement.
1. All objects in motion have
a) potential energy. b) heat energy.
c) kinetic energy.
d) random energy.
2. The first scientist to observe evidence of random motion in molecules was
a) Brown. b) Darwin. c) Mendel. d) Hooke.
3. Most of the cell and its surrounding environment are in a
a) solid solution. b) gaseous solution.
c) solid phase.
d) water solution.
4. The net movement of particles from an area of higher concentration to an
area of lower concentration is called
a) active transport. b) nonrandom movement.
c) osmosis.
d) diffusion.
5. Diffusion occurs because of
a) nonrandom movement of particles.
b) random movement of particles.
c) a chemical reaction between particles.
d) chemical energy.
6. When a few crystals of potassium permanganate are dropped into a
beaker of water, the ions of the dissolving compound will
a) move from low concentration to high concentration.
b) form a polar bond.
c) start to diffuse.
d) Remain on the bottom of the beaker.
7. When materials pass into and out of the cell at equal rates, there is no net
change in concentration inside the cell. The cell is in a state of
a) dynamic equilibrium. b) metabolism. c) imbalance. d) inertia
8. Oxygen diffuses into the capillaries of the lungs because there is a
a) lesser concentration of oxygen in the air sacs of lungs than in the
capillaries.
b) equal concentration of carbon dioxide in the air sacs of the lungs
and in the capillaries.
c) equal concentration of oxygen in the air sacs of the lungs and in the
capillaries.
d) greater concentration of oxygen in the air sacs of the lung than in
the capillaries.
9. The difference in concentration from one region to another is called
a) dynamic equilibrium. b) concentration gradient.
c) homeostasis.
d) Brownian movement.
10. Molecules of the following will not diffuse directly across the lipid bilayer:
a) an amino acid. b) carbon dioxide c) water. d) oxygen
Complete the table by checking the correct column for each statement.
Statement
The concentration of dissolved substances
outside the cell is lower than inside the
cell. The environment out side the cell is:
When a cell is placed in this type of
solution, water will enter the cell by
osmosis, resulting in turgor pressure.
The concentration of dissolved substances
is the same inside the cell as it is outside
the cell.
The concentration of the substances
outside the cell is greater than inside the
cell the environment is:
When injected into the body, it will not
cause cellular damage if what you are
injecting is _______ to the cell.
Putting a plant cell in this type of solution
will result in a loss of water, and a drop of
turgor pressure (or plasmolysis), which will
cause the cell to wilt.
Isotonic
Hypotonic Hypertonic
Answer the following questions.
1. If a cell is placed in a hypotonic solution what happens to the volume of
the cell? This affects what type of pressure? What affect would this have
on a plant?
2. What happens to a plant when it is deprived of water or is placed in a
hypertonic solution? What is this called?
Here are some lab reports that need help. Write a response to each report.
1. Experiments show that lipid molecules can pass across the plasma
membrane from an area of high concentration to low concentration. By
which process do the molecules move across the membrane? Does the
cell expend energy? Explain.
2. A biochemical test shows the passive transport of sugar molecules into a
muscle cell. What are the proteins embedded in the lipid bilayer that aid in
its movement called? What are the two main types?
3. In a nerve cell, sodium ions move across the membrane from an area of
lower concentration to an area of higher concentration. Does the nerve
cell expend energy? What type of transport is taking place?
4. An experiment reveals a carrier protein involved in active transport of an
amino acid across a membrane into a cell. Explain how the protein moves
the molecule across the gradient.